BACKGROUND OF THE INVENTION A typical refrigeration appliance has two separate compartments which are kept at different temperatures, at least a compressor for supplying refrigerant, and one or more evaporators over which the warm air from the compartments is circulated by means of fan. Fan draws the warmer air from the compartments and circulates it over the evaporator surfaces, and deliver colder air to the compartments. Circulation of warm air over the evaporators results in accumulation of frost on the evaporator, and decreases the efficiency of the refrigerator. Therefore, frost is melted periodically during a defrost cycle.

During the defrost cycle, the compressor stops and a heat source is activated. Commonly used heat source is a resistant heater. Use of resistant heaters increases energy consumption. Furthermore, efficiency of defrosting with resistant heaters are generally very low, around 30%, that means most of the energy is consumed for heating the cabinet instead of melting the frost.

In US Patent No. 5,406,805, two separate evaporators are utilized for each of the compartments.

Defrosting of fresh food evaporator is achieved by circulating the fresh food compartment air through evaporator by means of a fan when the compressor is off. The warm air defrosting process is only effective when the compressor is off. Since the compressor is off during the defrosting period, temperature in the fresh food compartment and especially in the freezer compartment may rise above the allowed limits due to the longer defrost duration when it is compared to defrosting with resistant heaters. Therefore, in order to ensure an effective defrost, a resistant heater is also used which decreases the benefits of air defrosting and increases cost as well.

SUMMARY OF INVENTION The object of this invention is to provide a method for efficiently defrosting a refrigeration appliance and a refrigeration appliance using thereof.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the defrosting method and the refrigerator using thereof., which is realised in order to attain the said object of the invention is illustrated in the attached drawings, wherein; Figure 1, is a schematic view of the cooling circuit for a system in which evaporators are arranged in series; Figure 2, is a schematic view of the cooling circuit for a system in which evaporators are arranged in parallel; The components shown in the drawings have been enumerated individually, as follows; 1-Compressor 2-Condenser 3-Filter-dryer 4a-capillary tube for first sub evaporator 4b-capillary tube for second sub evaporator 4c-capillary tube for freezer evaporator) 5-Suction line heat exchanger 6-Freezer Evaporator 7-Freezer Fan 8-Solenoid valve 9-Fresh food fan 10-First sub-evaporator 11-Second sub-evaporator 12-Separator 13-Drain tray

14-Suction line 15-Drain hole for first sub evaporator 16-Drain hole for second sub evaporator 17-Freezer compartment 18-Fresh food compartment 19-Check valve 20-Fresh food evaporator DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical refrigeration appliance, cooled with the circulation of a refrigerant having multiple refrigeration compartments, specifically a fresh food compartment (18) and a freezer compartment (17), comprises a compressor (1) for pressurizing the refrigerant vapour to increase the pressure and temperature of the refrigerant, a condenser (2) for condensing the refrigerant, a filter-dryer (3) for capturing the moisture and impurities of the refrigerant, a capillary tube (4) for decreasing the pressure and thus the temperature of the refrigerant, a suction line heat exchanger (5), a fresh food evaporator (20) for cooling the fresh food compartment (18) and a fresh food fan (9) for circulating air over the fresh food evaporator (20), a freezer evaporator (6) for cooling the freezer compartment (17) and a freezer fan (7) for circulating air over the freezer evaporator (6) and a suction line (14) for turning the refrigerant back to the compressor (1).

The fresh food evaporator (20) and the freezer evaporator (6) can be arranged either in series or in parallel. In series arrangement, the refrigerant first circulates through one of the evaporators then through the other, whereas in parallel arrangement, the refrigerant goes through the evaporators independently. In order to cool the compartments (17 and 18), the compressor (1) is turned on and off. If the temperature in the freezer cabinet (17) is high, the compressor (1) and the freezer fan (7) are turned on. While the compressor (1) is on, if the fresh food cabinet (18) temperature is high, the fresh food fan (9) is activated.

In the preferred embodiment of the present invention, the freezer evaporator (6) and the fresh food evaporator (20) are arranged in series. Therefore, the refrigerant preferably first goes through the fresh food evaporator (20) and then the freezer evaporator (6).

In the refrigeration appliance of the present invention, the fresh food evaporator (20) is composed of more than one sub-evaporator that are arranged in parallel. Preferably, there are two sub- evaporators namely a first sub-evaporator (10) and a second sub-evaporator (11). Sub-evaporators (10 and 11) are arranged in parallel and both of the sub-evaporators (10 and 11) are used sequentially for cooling the fresh-food compartment.

The refrigeration appliance further comprises a separator (12) for isolating the first sub-evaporator (10) and the second sub-evaporator (11) from each other, a solenoid valve (8), preferably a bi-stable valve, for directing the refrigerant to one of the sub-evaporators (10 and 11) and two capillary tubes (4a and 4b) for decreasing the pressure and thus the temperature of the refrigerant that is supplied to the first and second sub evaporators (10 and 11) respectively.

During a cooling cycle, the refrigerant is pressurised by the compressor (1) and fed into the condenser (2). Through the condenser (2), refrigerant exchanges heat with the ambient air and condenses. Refrigerant then goes through the filter-dryer (3) and the solenoid valve (8) which directs the refrigerant to the preferred sub-evaporator (10 or 11) through the respective capillary (4a or 4b). The capillaries (4a and 4b) for creating heat exchange between the capillary tube (4) and the suction line (14), goes through the heat exchanger (5). Concurrently the fresh food compartment fan (9), draws warm air from the fresh food compartment (18). Warm air passes over the fresh food sub evaporators (10 and 11), cools down and then returns to the fresh food compartment (18).

After the fresh food evaporator (20), refrigerant goes through the freezer evaporator (6) where freezer cabinet is cooled by means of cold air circulated by freezer fan (7). Then refrigerant goes to the heat exchanger (5) and suction line (14). Refrigerant completes its cycle when it returns to the compressor (1) again.

During the cooling cycle, refrigerant is directed to one of the sub-evaporators (10 and 11). Solenoid valve (8), for a predetermined defrost duration tdefl, directs the refrigerant only to the first sub- evaporator (10). During the circulation of air over the sub-evaporators (10 and 11) frost accumulates only on the first sub evaporator surface (10) in which refrigerant is fed through.

During the predetermined defrost duration tdefl if the fresh food fan (9) is operating, warm air is circulated over both of the sub-evaporators (10 and 11). Warm air helps defrosting of the second sub evaporator (11) which is in rest position i. e. refrigerant is not fed through. In the mean time, warm air is cooled by the first sub-evaporator (10). After the duration tdefl, the same steps are

repeated for defrosting the first sub-evaporator (10). This time, the solenoid valve (8), for the duration tdef2,, directs the refrigerant only to the second sub-evaporator (11). During the circulation of air over the fresh food evaporators (10 and 11) frost accumulates only on the second sub evaporator surface (11) in which refrigerant is fed through. During the predetermined tdef2 defrost duration if the fresh food fan (9) is active, warm air is circulated over both of the sub- evaporators (10 and 11). Warm air travels over the first sub-evaporator (10) and helps frost melting.

In the mean time, warm air is cooled by the second sub-evaporator (11).

Since no additional resistant heaters or other means are used for defrosting, the predetermined defrost duration is experimentally optimized for allowing the complete defrost of the sub- evaporators (10 or 11). This enables continuous cooling of the fresh food compartment (18) and defrosting of the fresh food evaporator (20) concurrently.

The sub-evaporators (10 and 11) are isolated with the separator (12) which is preferably made of styrofoam and covered with an aluminium folio which keeps moisture away from the styrofoam material and avoiding hygiene problems. The separator (12) does not interfere the airflow, but prevents the air shortcuts between evaporators. Air is always circulated over both of the sub- evaporators (10 and 11) regardless of which one is in operation. The separator (12) will be high enough to establish a natural barrier so that cold air does not move to the other side to and create frosting. This situation is likely to happen provided that the fresh food compartment (18) temperature is low, the fresh food fan (9) is in off position and one of the sub-evaporators (10 and 11) is still in operation. Because of the separator (12), cold air will be trapped in its volume so that frosting problems in neighbouring evaporator will be eliminated.

The refrigeration appliance further comprises a drain tray (13) for collecting the defrost water during the defrosting and two separate drain holes (15 and 16) for each sub-evaporators (10 and 11) for allowing easy drainage of water without having affecting the other.

In another embodiment of the present invention, the freezer evaporator (6) and the fresh food evaporator (20) are arranged in parallel. Therefore, the refrigerant either goes through the fresh food evaporator (20) or the freezer evaporator (6). In parallel arrangement, the refrigeration appliance further comprises a capillary tube (4c) for decreasing the pressure and the temperature of the refrigerant that is supplied to the freezer evaporator (6) and a check valve (19) for avoiding the back flow of the refrigerant to the freezer evaporator (6).

In this alternative embodiment, the refrigerant after the filter-dryer (3) is directed either to the fresh food evaporator (20) or to the freezer evaporator (6). The defrosting method of the sub-evaporators (10 and 11) is the same. The refrigerant after leaving the sub-evaporators (10 and 11) directly goes to the suction line (14).

During a cooling cycle, the refrigerant is pressurised by the compressor (1) and fed to the condenser (2). Through the condenser (2), refrigerant exchanges heat with the ambient air and condenses.

Refrigerant then goes through the filter-dryer (3) and solenoid valve (8) which directs the refrigerant to one of the sub-evaporator (10 or 11) or to the freezer evaporator (6) through the respective capillary (4a, 4b or 4c). The capillaries (4a, 4b and 4c) go through the heat exchanger (5). Concurrently the fresh food compartment fan (9) draws warm air from the fresh food compartment (18). Warm air passes over the fresh food sub evaporators (10 and 11), and cools down, then returns to the fresh food compartment (18). During the circulation of air over the fresh food evaporators (10 or 11), frost accumulates on the evaporator surfaces and that decreases the efficiency of the refrigeration appliance.

The refrigerant after leaving the sub-evaporators (10 and 11) or the freezer evaporator (6) goes to the suction line (14). The check valve (19) prevents back flows through the freezer evaporator (6) when one of the sub-evaporators (10 or 11) is in operation and the freezer evaporator (6) is in off position. Refrigerant completes its cycle when it returns to the compressor (1) again.

During the cooling cycle, refrigerant is directed to one of the sub-evaporators (10 and 11). Solenoid valve (8), for a predetermined defrost duration tdefl, directs the refrigerant only to the first sub- evaporator (10). During the circulation of air over the sub-evaporators (10 and 11) frost accumulates only on the first sub evaporator surface (10) in which refrigerant is fed through.

During the predetermined defrost duration tdefl if the fresh food fan (9) is operating, warm air is circulated over both of the sub-evaporators (10 and 11). Warm air helps defrosting of the second sub evaporator (11) which is in rest position i. e. refrigerant is not fed through. In the mean time, warm air is cooled by the first sub-evaporator (10). After the duration tdefl, the same steps are repeated for defrosting the first sub-evaporator (10). This time, the solenoid valve (8), for the duration tdef2,, directs the refrigerant only to the second sub-evaporator (11). During the circulation of air over the fresh food evaporators (10 and 11) frost accumulates only on the second sub evaporator surface (11) in which refrigerant is fed through. During the predetermined tdef2

defrost duration if the fresh food fan (9) is operating, warm air is circulated over both of the sub- evaporators (10 and 11). Warm air travels over the first sub-evaporator (10) and helps frost melting.

In the mean time, warm air is cooled by the second sub-evaporator (11).

The refrigeration appliance of the current invention eliminates the use of electrical heaters for the defrosting of fresh food evaporators, thus, decreases the energy consumption while providing a satisfactory cooling.